The process according to the invention originates from a technique consisting of only fluidizing the lower layers of the moving or semi-moving or fixed bed so as to discharge more easily the catalyst particles, the upper layers of the catalyst bed remaining as moving bed or fixed bed. U.S. Pat. No. 3 716 478 teaches a similar principle whereby a correct fluidization is achieved at the bottom of the reactor by acting on the charge feed rate at the reactor bottom and by transporting, generally through a pump, the catalyst particles for discharging them from the reactor. However, in this above mentioned U.S. patent, the paths of the catalyst particles are irregular and difficult to control and hence produce an irregular flow, not compatible with the required progressive lowering of the whole bed in the reactor ; these disadvantages are strengthened when using a reactor of large diameter, more and more used in refining operations.
The present invention meets a need of simplification and particularly relates to reactors of very large diameters.